Influenza has a long history characterized by waves of pandemics, epidemics, resurgences and outbreaks. Influenza is a highly contagious disease that could be equally devastating both in developing and developed countries. The influenza virus presents one of the major threats to the human population. In spite of annual vaccination efforts, influenza infections result in substantial morbidity and mortality. Although flu epidemics occur nearly every year, fortunately pandemics do not occur very often. However, recent flu strains have emerged such that we are again faced with the potential of an influenza pandemic. Avian influenza virus of the type H5N1, currently causing an epidemic in poultry in Asia as well as regions of Eastern Europe, has persistently spread throughout the globe. The rapid spread of infection, as well as cross species transmission from birds to human subjects, increases the potential for outbreaks in human populations and the risk of a pandemic. The virus is highly pathogenic, resulting in a mortality rate of over fifty percent in birds as well as the few human cases which have been identified. If the virus were to achieve human to human transmission, it would have the potential to result in rapid, widespread illness and mortality.
Subtypes of the influenza virus are designated by different HA and NA resulting from antigenic shift. Furthermore, new strains of the same subtype result from antigenic drift, or mutations in the HA or NA molecules which generate new and different epitopes. While technological advances have improved the ability to produce improved influenza antigens vaccine compositions, there remains a need to provide additional sources of protection against to address emerging subtypes and strains of influenza.